The present invention relates to audio cables in general and in particular to a method and apparatus comprising a passive network particularly suitable for use in cables designed to connect electrical musical instruments to amplifiers.
Musicians of electrical instruments have long been aware that the audio qualities of their music depend in part on the total system comprising the instrument, the cable and the amplifier. Generally, within the range of audio frequencies produced by a particular electrical instrument, cable and amplifier system, there is a smaller range in which the sounds produced are “emphasized” or “noisy.” The actual range depends on the length, materials and construction of the cable.
Graphic equalizers, which utilize active filters, may be used to compensate for this effect. Usually the compensation requires an amplification of the sounds at the lower and higher end of the relevant frequency range, with a gradual decrease in the amplification for each frequency range toward the center frequency which produces the familiar “V” on the graphic equalizer controls. Active filter compensation, however, can produce its own noise. Furthermore, a more evenly balanced signal expands the control choices afforded to the musician by a graphic equalizer. Because of the required compensation, such choices are usually limited in current standard systems.
The inventors of the present invention discovered that there was a relationship between the rate of change in the phase angle of the cable and the perceived clarity and “evenness” of the music produced by the system. Where the rate of change in the phase angle was at a maximum the sound produced was the most “emphasized” or “noisy.” The relationship could be quantified in terms of the frequency at which the positive conductor of the cable had a phase angle of 45° (or, alternatively, as the frequency where the quality factor (Q) was equal to 1) as a result of the inherent inductance of the cable.
The inventors discovered that by selectively connecting passive RC or RLC circuits between the positive and negative (or ground) conductors of the cable, where the RC or RLC circuits had a phase angle of −45° at selected frequencies that were within the audio frequency range, approximately equally distributed on a logarithmic scale, and not equal to the frequency where the cable naturally had a phase angle of 45°, the resulting audio output could be modified to significantly reduce the “emphasized” or “noisy” effect, and produce a more uniform audio output over the range of frequencies produced by the system.